Use ESM

.gitignore

@@ -1,8 +1,5 @@
 .DS_Store
 *.log
-.nyc_output/
 coverage/
 node_modules/
-nlcst-test.js
-nlcst-test.min.js
 yarn.lock

.prettierignore

@@ -1,5 +1,2 @@
 coverage/
-nlcst-test.js
-nlcst-test.min.js
-*.json
 *.md

index.js

@@ -1,48 +1,73 @@
-'use strict'
-
-var assert = require('assert')
-var zwitch = require('zwitch')
-var mapz = require('mapz')
-var unist = require('unist-util-assert')
-
-var nlcst = zwitch('type')
-
-exports = unist.wrap(nlcst)
-module.exports = exports
-
-exports.parent = unist.wrap(parent)
-exports.text = unist.text
-exports.void = unist.void
-exports.wrap = unist.wrap
-exports.all = mapz(exports, {key: 'children', indices: false})
-
-// Core interface.
-nlcst.unknown = unknown
-nlcst.invalid = unknown
-
-// Per-type handling.
-nlcst.handlers = {
-  RootNode: unist.wrap(RootNode),
-  ParagraphNode: exports.parent,
-  SentenceNode: exports.parent,
-  WordNode: exports.parent,
-  TextNode: exports.text,
-  SymbolNode: exports.text,
-  PunctuationNode: exports.text,
-  WhiteSpaceNode: exports.text,
-  SourceNode: exports.text
+import nodeAssert from 'assert'
+import {zwitch} from 'zwitch'
+import {mapz} from 'mapz'
+import {
+  assert as unistAssert,
+  parent as unistParent,
+  literal,
+  _void,
+  wrap
+} from 'unist-util-assert'
+
+/**
+ * Assert that `node` is a valid nlcst node.
+ * If `node` is a parent, all children will be asserted too.
+ *
+ * @param {unknown} [node]
+ * @param {Parent} [parent]
+ * @returns {asserts node is Node}
+ */
+export function assert(node, parent) {
+  return wrap(nlcst)(node, parent)
+}
+
+/**
+ * Assert that `node` is a valid nlcst parent.
+ *
+ * @param {unknown} [node]
+ * @param {Parent} [parent]
+ * @returns {asserts node is Parent}
+ */
+export function parent(node, parent) {
+  return wrap(assertParent)(node, parent)
 }
 
+export {literal, _void, wrap}
+
+var all = mapz(assert, {key: 'children'})
+
+var nlcst = zwitch('type', {
+  // Core interface.
+  unknown,
+  invalid: unknown,
+  // Per-type handling.
+  handlers: {
+    RootNode: wrap(RootNode),
+    ParagraphNode: parent,
+    SentenceNode: parent,
+    WordNode: parent,
+    TextNode: literal,
+    SymbolNode: literal,
+    PunctuationNode: literal,
+    WhiteSpaceNode: literal,
+    SourceNode: literal
+  }
+})
+
 function unknown(node, ancestor) {
-  unist(node, ancestor)
+  unistAssert(node, ancestor)
 }
 
-function parent(node) {
-  unist.parent(node)
-  exports.all(node)
+function assertParent(node) {
+  unistParent(node)
+  all(node)
 }
 
 function RootNode(node, ancestor) {
   parent(node)
-  assert.strictEqual(ancestor, undefined, '`RootNode` should not have a parent')
+  nodeAssert.strictEqual(
+    ancestor,
+    undefined,
+    '`RootNode` should not have a parent'
+  )
 }

package.json

@@ -23,32 +23,30 @@
   "contributors": [
     "Titus Wormer <tituswormer@gmail.com> (https://wooorm.com)"
   ],
+  "sideEffects": false,
+  "type": "module",
+  "main": "index.js",
   "files": [
     "index.js"
   ],
   "dependencies": {
-    "mapz": "^1.0.0",
-    "unist-util-assert": "^2.0.0",
-    "zwitch": "^1.0.0"
+    "mapz": "^2.0.0",
+    "unist-util-assert": "^3.0.0",
+    "zwitch": "^2.0.0"
   },
   "devDependencies": {
-    "browserify": "^17.0.0",
-    "nyc": "^15.0.0",
+    "c8": "^7.0.0",
     "prettier": "^2.0.0",
     "remark-cli": "^9.0.0",
     "remark-preset-wooorm": "^8.0.0",
     "tape": "^5.0.0",
-    "tinyify": "^3.0.0",
-    "xo": "^0.38.0"
+    "xo": "^0.39.0"
   },
   "scripts": {
     "format": "remark . -qfo && prettier . -w --loglevel warn && xo --fix",
-    "build-bundle": "browserify . -s nlcstTest -o nlcst-test.js",
-    "build-mangle": "browserify . -s nlcstTest -o nlcst-test.min.js -p tinyify",
-    "build": "npm run build-bundle && npm run build-mangle",
-    "test-api": "node test",
-    "test-coverage": "nyc --reporter lcov tape test",
-    "test": "npm run format && npm run build && npm run test-coverage"
+    "test-api": "node test/index.js",
+    "test-coverage": "c8 --check-coverage --branches 100 --functions 100 --lines 100 --statements 100 --reporter lcov node test/index.js",
+    "test": "npm run format && npm run test-coverage"
   },
   "prettier": {
     "tabWidth": 2,
@@ -60,16 +58,10 @@
   },
   "xo": {
     "prettier": true,
-    "esnext": false,
-    "ignores": [
-      "nlcst-test.js"
-    ]
-  },
-  "nyc": {
-    "check-coverage": true,
-    "lines": 100,
-    "functions": 100,
-    "branches": 100
+    "rules": {
+      "no-var": "off",
+      "prefer-arrow-callback": "off"
+    }
   },
   "remarkConfig": {
     "plugins": [

readme.md

@@ -12,6 +12,9 @@
 
 ## Install
 
+This package is [ESM only](https://gist.github.com/sindresorhus/a39789f98801d908bbc7ff3ecc99d99c):
+Node 12+ is needed to use it and it must be `import`ed instead of `require`d.
+
 [npm][]:
 
 ```sh
@@ -21,7 +24,7 @@ npm install nlcst-test
 ## Use
 
 ```js
-var assert = require('nlcst-test')
+import {assert} from 'nlcst-test'
 
 assert({type: 'RootNode', children: []})
 assert({type: 'SourceNode', value: 'fn()'})
@@ -37,13 +40,16 @@ assert({type: 'WordNode', value: 'foo'})
 
 ## API
 
+This package exports the following identifiers: `assert`, `parent`, `literal`,
+`_void`, and `wrap`.
+There is no default export.
+
 ### `assert(tree)`
 
 Assert that [`tree`][tree] is a valid [nlcst][] [node][].
 If `tree` is a [parent][], all [child][]ren will be asserted as well.
 
-The `assert.parent`, `assert.text`, `assert.void`, and `assert.wrap`
-methods from [`unist-util-assert`][unist-util-assert] are also included.
+The other methods come from [`unist-util-assert`][unist-util-assert].
 
 ## Related
 

test/children.js

@@ -1,7 +1,5 @@
-'use strict'
-
-var test = require('tape')
-var assert = require('..')
+import test from 'tape'
+import {assert} from '../index.js'
 
 test('children', function (t) {
   t.throws(

test/index.js

@@ -1,7 +1,5 @@
-'use strict'
-
 /* eslint-disable import/no-unassigned-import */
-require('./node')
-require('./children')
-require('./root')
+import './node.js'
+import './children.js'
+import './root.js'
 /* eslint-enable import/no-unassigned-import */

test/node.js

@@ -1,7 +1,5 @@
-'use strict'
-
-var test = require('tape')
-var assert = require('..')
+import test from 'tape'
+import {assert} from '../index.js'
 
 test('node', function (t) {
   t.throws(

test/root.js

@@ -1,7 +1,5 @@
-'use strict'
-
-var test = require('tape')
-var assert = require('..')
+import test from 'tape'
+import {assert} from '../index.js'
 
 test('assert(RootNode)', function (t) {
   t.throws(